1. Field of the Invention
The present invention relates generallY to an improved apparatus for mixing gas and liquid and more particularly to an improved apparatus as characterized which includes an ejector.
2. Description of the Prior Art
Among the known gas-liquid mixing methods are those typified by the use of a perforated plate and an ejector. In the perforated plate method, a gas is passed through a perforated member, such as a porous plate or a cylinder, which is dipped in a liquid, to cause mixing of the gas therein as fine bubbles. On the other hand, in the ejector method, a compressed liquid is fed to a nozzle of an ejector to cause mixing of a gas therewith by aspirating the gas under negative pressure around the jet stream of the liquid flowing from the nozzle at high velocity.
The ejector method may be considered to have advantages over the perforated plate method from the viewpoint that fine bubbles are formed therein and because the perforated plate method requires a compressed gas. whereas the ejector method can be operated under atmospheric pressure without need of a compressed gas. Accordingly, the ejector method is preferably employed. However, the ejector method also has certain disadvantages, such as occurs when the feed rate of the gas being fed from the gas feeder is lower than the aspirating volume rate of the ejector, in which case the pressure of the gas feed system, including the gas feeder, decreases to cause trouble. That is, there is a possibility that a counterflow of the liquid from the gas aspirating inlet of the ejector to the gas feed system will develop after the termination of the operation of the ejector. Generally, a structure is provided for preventing such counterflow, such as an electromagnetic valve or other check valve, even though the gas feed system is in negative pressure. However, it often happens that this valve is not properly actuated, in which case, such counterflow is not always prevented.